The invention relates to mounted assemblies for aircraft and to the wheels and tires which constitute them. The mounted assemblies for aircraft to which the invention relates are characterized in particular by the combination of an inflation pressure greater than 9 bar and a relative deflection of the tire greater than 30%.
The deflection of a tire is defined by the radial deformation of the tire, or variation in the radial height, when it changes from a non-loaded state to a statically loaded state, under rated load and pressure conditions.
It is expressed in the form of a relative deflection, defined by the ratio of this variation in the radial height of the tire to half the difference between the external diameter of the tire and the maximum diameter of the rim measured on the hook. The external diameter of the tire is measured statically in a non-loaded state at the rated pressure.
The reinforcement armature or reinforcement of tires and in particular of aircraft tires is currently—and most frequently—formed by a ply or a stack of several plies conventionally referred to as “carcass plies”, “crown plies”, etc. This manner of designating the reinforcement armatures derives from the manufacturing process, which consists of producing a series of semi-finished products in the form of plies, provided with cord reinforcing threads which are frequently longitudinal, which are subsequently assembled or stacked in order to build a tire blank. The plies are produced flat, with large dimensions, and are subsequently cut according to the dimensions of a given product. The plies are also assembled, in a first phase, substantially flat. The blank thus produced is then shaped to adopt the toroidal profile typical of tires. The semi-finished products referred to as “finishing” products are then applied to the blank, so as to obtain a product ready to be vulcanized.
Such a type of “conventional” process involves, in particular for the phase of manufacture of the blank of the tire, the use of an anchoring element (generally a bead wire), used for anchoring or holding the carcass reinforcement in the zone of the beads of the tire. Thus, in this type of process, a portion of each of the plies constituting the carcass reinforcement (or only a part thereof) is turned up around a bead wire arranged in the tire bead. In this manner, the carcass reinforcement is anchored in the bead.
The fact that this conventional type of process has become more widespread in the industry, despite numerous variants in the manner of producing the plies and assemblies, has led the person skilled in the art to use a vocabulary modeled on the process; hence the generally accepted terminology, comprising in particular the terms “plies”, “carcass”, “bead wire”, “shaping” to designate the change from a flat profile to a toroidal profile, etc.
There are nowadays tires which do not, properly speaking, comprise “plies” or “bead wires” in accordance with the preceding definitions. For example, document EP 0 582 196 describes tires manufactured without the aid of semi-finished products in the form of plies. For example, the reinforcement elements of the different reinforcement structures are applied directly to the adjacent layers of rubber mixes, the whole being applied in successive layers to a toroidal core the form of which makes it possible to obtain directly a profile similar to the final profile of the tire being manufactured. Thus, in this case, we no longer find “semi-finished products”, nor “plies”, nor “bead wires”. The base products, such as the rubber mixes and the reinforcement elements in the form of cords or filaments, are applied directly to the core. As this core is of toroidal form, the blank no longer has to be shaped in order to change from a flat profile to a profile in the form of a torus.
Furthermore, the tires described in this document do not have the “conventional” upturn of the carcass ply around a bead wire. This type of anchoring is replaced by an arrangement in which circumferential cords are arranged adjacent to said sidewall reinforcement structure, the whole being connected by an anchoring or bonding rubber mix.
There are also processes for assembly on a toroidal core using semi-finished products, such as strips, specially adapted for quick, effective and simple laying on a central core. Finally, it is also possible to use a mixture comprising at the same time certain semi-finished products to produce certain architectural aspects (such as plies, bead wires, etc.), whereas others are produced from the direct application of mixes and/or reinforcement elements.
In the present document, in order to take into account recent technological developments both in the field of manufacture and in the design of products, the conventional terms such as “plies”, “bead wires”, etc., are advantageously replaced by neutral terms or terms which are independent of the type of process used. Thus, the term “carcass-type reinforcing thread” or “sidewall reinforcing thread” is valid as a designation for the reinforcement elements of a carcass ply in the conventional process, and the corresponding reinforcement elements, generally applied at the level of the sidewalls, of a tire produced in accordance with a process without semi-finished products. The term “anchoring zone”, for its part, may equally well designate the “traditional” upturn of a carcass ply around a bead wire of a conventional process and the assembly formed by the circumferential reinforcement elements, the rubber mix and the adjacent sidewall reinforcement portions of a bottom zone produced with a process using application on a toroidal core.
Hereafter, “axial” is understood to mean a direction parallel to the axis of rotation of the tire; this direction may be “axially inner” when it is directed towards the inside of the tire and “axially outer” when it is directed towards the outside of the tire.
“Radial” is understood to mean a direction perpendicular to the axis of rotation of the tire and passing through this axis of rotation. This direction may be “radially inner” or “radially outer” depending on whether it is directed towards the axis of rotation or towards the outside of the tire.
“A radially oriented reinforcement element” is understood to mean a reinforcement element contained substantially within one and the same axial plane.
“A circumferentially oriented reinforcement element” is understood to mean a reinforcement element oriented substantially parallel to the circumferential direction of the tire, that is to say forming with this direction an angle which does not diverge by more than five degrees from the circumferential direction.
“Reinforcement element” is understood to mean equally well monofilaments and multifilaments, or assemblies such as cables, plied yarns or alternatively any equivalent type of assembly, whatever the material and the treatment of these reinforcement elements, for example surface treatment or coating or pre-sizing in order to promote adhesion to the rubber.
“Contact” between a reinforcement element and an anchoring rubber mix is understood to mean the fact that at least part of the outer circumference of the reinforcement element is in intimate contact with the anchoring rubber mix; if a reinforcement element comprises a covering or a coating, the term “contact” means that it is the outer circumference of this covering or coating which is in intimate contact with the anchoring rubber mix
“Elasticity modulus” of a rubber mix is understood to mean a secant modulus of extension at 10% deformation and at ambient temperature; the measurement is effected after a first accommodation cycle up to 10% deformation:
                              -                      E            10                          =                ⁢                                            F              10                                      S              ×                              ɛ                10                                              ⁢                      i            .            e            .                                                            E          10                =                ⁢                                                            F                10                            ⁡                              (                                  1                  +                                      ɛ                    10                                                  )                                                                    S                0                            ×                              ɛ                10                                              ⁢                                          ⁢          and                                                  E          10                =                ⁢                                            F              10                        ×            1.1                                              S              0                        ×            0.1                              in which ε10 is equal to 0.1; with E10: secant modulus of extension at 10% deformation; F10: tensional force at 10% extension; S0: initial section of the test piece; S: section of the test piece at the deformation of extension ε; in the case of rubber material, it is known that:
      S    =                  S        0                    1        +        ɛ              ;and ε10: deformation of extension at 10%. The measurements of elasticity modulus of a rubber mix are carried out under tension in accordance with Standard AFNOR-NFT-46002 of September 1988: the nominal secant modulus (or apparent stress, in MPa) at 10% elongation is measured in a second elongation (i.e. after an accommodation cycle) (normal conditions of temperature and relative humidity in accordance with Standard AFNOR-NFT-40101 of December 1979).
“Tg” of an elastomer is understood to mean the glass transition temperature thereof measured by differential thermal analysis.
“Static creep test” is understood to mean a test in which test pieces are prepared, the useful part of which has a length of 70 mm, a width of 5 mm and a thickness of 2.5 mm (these test pieces are cut from vulcanized sheets of a thickness of 2.5 mm); the test pieces are placed in an oven at 150° C. and a 3 kg weight is immediately hung from them; the test is thus carried out with an initial stress of:
      σ    0    =            Mg              S        0              =          2.35      ⁢                          ⁢      MP      ⁢                          ⁢      a      with M: weight applied, g: gravity acceleration and S0: initial section of the test piece being measured; the elongation of the useful part of the test piece is measured as a function of time; the “amount of static creep” corresponds to the variation of deformation over a given time, for example between 3 and 5 hours' testing:
  τ  =            Δ      ⁢                          ⁢      ɛ              Δ      ⁢                          ⁢      t      where: Δε=ε(t2)−ε(t1) variation in the deformation measured during Δt=t2−t1 in minutes (min).
“Rheometry test” is understood to mean an alternating shearing test at a deformation of ±0.2 degrees, a frequency of 100 cycles/min, a temperature of 197° C. and a duration of 10 min; rheometer from Monsanto; the test is performed on a disc of uncured mix, the change over the 10 min. in the torque resulting from the shearing imposed between the two faces of the disc is recorded; the change in the torque after the maximum measured will be particularly noted here: if the torque measured remains stable, there is no reversion, that is to say, reduction in the stiffness of the test piece; if the torque measured decreases, it indicates that there is reversion; the phenomenon of reversion results in a reduction in the rigidity of the test piece under the test conditions; it is a test of the thermal stability of the mix at high temperature;
  r  =                              C          max                -                  C          10                            C        max              ×    100  is the amount of reversion at the end of the test; Cmax is the maximum torque measured and C10 is the torque measured after 10 minutes' testing.
As far as the cords or metal cables are concerned, the measurements of breaking load (maximum load in N), tensile strength (in MPa) and elongation at break (total elongation in %) are carried out under tension in accordance with Standard ISO 6892 of 1984.
As far as the cords or textile cables are concerned, the mechanical properties are measured on fibers which have been subjected to prior conditioning. “Prior conditioning” is understood to mean storage of the fibers for at least 24 hours, before measurement, in a standard atmosphere in accordance with European Standard DIN EN 20139 (temperature of 20±2° C.; relative humidity of 65±2%). The mechanical properties in extension (tenacity, modulus, elongation and energy at break) are measured in known manner using a ZWICK GmbH & Co (Germany) 1435-type or 1445-type tension machine. The fibers, after receiving a slight prior protective twist (helix angle of approximately 6°), are subjected to traction over an initial length of 400 mm at a nominal speed of 200 mm/min. All the results are an average of 10 measurements.
The tires may, as previously mentioned, have different types of construction.
U.S. Pat. No. 4,832,102 for example describes an aircraft tire comprising a crown, two sidewalls and two beads, a carcass reinforcement and a crown reinforcement in which the carcass reinforcement comprises two circumferential alignments of reinforcing threads of high elasticity modulus, anchored in the two beads, and the crown reinforcement comprises at least one working block with at least one ply of reinforcing threads of high elasticity modulus. The carcass reinforcement is anchored in the beads by turning up, around a bead wire, the two circumferential alignments of first reinforcing threads of high elasticity modulus.
Patent WO 02/00456 describes a different type of aircraft tires the carcass reinforcement of which comprises two or three circumferential alignments of reinforcement elements of high elasticity modulus and anchoring means of said reinforcement elements, constituting the carcass reinforcement, within each bead. The anchoring means in accordance with this document are formed of circumferentially oriented cords axially bordering the circumferential alignments of the reinforcement elements of the carcass reinforcement, said reinforcement elements of the carcass reinforcement and the circumferentially oriented cords being separated by a bonding rubber mix of very high elasticity modulus. The use of cords makes it possible to obtain satisfactory rigidity with a bulk of the bead which is reduced as much as possible; the compactness of the bead is of paramount importance for aircraft tires to reduce the consequences of heating of said beads.
Aircraft tires must withstand extreme conditions during service, in particular in terms of applied load and speed, taking into account their low weight and size. As a result, despite their very high inflation pressures, greater than 9 bar, their loading or deflection during operation may commonly reach values double those observed for heavy-vehicle tires or passenger-car tires.
During takeoff, very high speeds, of the order of 350 km/hour or even 450 km/hour, are achieved, and hence the heating conditions are also very harsh.
All these conditions are particularly disadvantageous for the endurance of the beads of these tires.
These conditions are also restricting with regard to the holding of the tires on the rim. They have hitherto resulted in tires comprising an extremely rigid bottom zone or bead zone which permits good holding on said rim. This rigidity of the bottom zone of the tire consequently necessitates rims made in several parts which permit mounting and demounting of the aircraft tires.
Furthermore, the mounted assemblies thus produced for aircraft require strict, rigorous and frequent examination. These inspections may be accompanied by demounting of the mounted assembly and dissociation of the wheel and of the tire. These technical operations are longwinded and require action by a highly-qualified workforce.
The particular aim of the invention is a mounted assembly or tire-wheel assembly for aircraft which facilitates these technical inspections and more particularly which facilitates demounting and remounting of the mounted assemblies during the life of an aircraft tire.